Paper Title

Presenter Information

Presentation Type

Paper (supporting PowerPoints may be added as Additional Files)

Location

Bass Auditorium

Start Date

26-2-2019 3:45 PM

Abstract

There are two ways in which the collision risk between two space objects, as assessed by the probability of collision (Pc), can be considered low. The first and much more desirable way is when the predicted positions of the two satellites at their time of closest approach (TCA) are known with high certainty: a low Pc calculated under such circumstances means that one can conclude with a high degree of confidence that the miss distance at TCA is greater than the satellites’ combined size (the “hard-body radius”) and therefore that the two satellites are highly unlikely to collide. The second and more problematic way is when the predicted positions at TCA are known with very little certainty (the so-called “dilution region”): the resultant Pc is low not because the actual miss distance is almost certainly larger than the HBR but because so little is known about the satellites’ actual positions at TCA that a huge range of potential miss distances is possible, only a small portion of which are smaller than the HBR. While a large Pc in this latter case would indicate a potentially dangerous situation, a small Pc does not necessarily convey safety but only a lack of definitive information.

Alfano (2005) is credited with first bringing this phenomenon prominently into the literature; and since that time a number of researchers have addressed the issue in different ways, including not considering it a crippling operational problem (Frisbee 2009), seeing it as a complete statistical failure on the part of CA practitioners (Balch 2016, 2018), and respecting the utility of the Pc but advancing the need for additional metrics in order to respond properly in such situations (Carpenter et al., 2017). In light of these varied research results, some sort of assimilation/adjudication of these disparate positions and practical guidance is needed for CA operators.

The present paper seeks to illuminate the situation by addressing the following points:

Clarification of the actual philosophical positions of CA practitioners and intent of on-orbit CA activities, and the way this posture affects the use of dilution-region data in decision support;

Examination of some of the proposed alternatives to the use of the Pc for dilution-region situations and their operational viability; and

Treatment of how more, and more frequent, tracking data might ameliorate the situation, and what parts of the problem are likely to abide even with such improvements.

The paper will conclude with a set of recommendations for handling “dilution region” situations operationally.

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There are two ways in which the collision risk between two space objects, as assessed by the probability of collision (Pc), can be considered low. The first and much more desirable way is when the predicted positions of the two satellites at their time of closest approach (TCA) are known with high certainty: a low Pc calculated under such circumstances means that one can conclude with a high degree of confidence that the miss distance at TCA is greater than the satellites’ combined size (the “hard-body radius”) and therefore that the two satellites are highly unlikely to collide. The second and more problematic way is when the predicted positions at TCA are known with very little certainty (the so-called “dilution region”): the resultant Pc is low not because the actual miss distance is almost certainly larger than the HBR but because so little is known about the satellites’ actual positions at TCA that a huge range of potential miss distances is possible, only a small portion of which are smaller than the HBR. While a large Pc in this latter case would indicate a potentially dangerous situation, a small Pc does not necessarily convey safety but only a lack of definitive information.

Alfano (2005) is credited with first bringing this phenomenon prominently into the literature; and since that time a number of researchers have addressed the issue in different ways, including not considering it a crippling operational problem (Frisbee 2009), seeing it as a complete statistical failure on the part of CA practitioners (Balch 2016, 2018), and respecting the utility of the Pc but advancing the need for additional metrics in order to respond properly in such situations (Carpenter et al., 2017). In light of these varied research results, some sort of assimilation/adjudication of these disparate positions and practical guidance is needed for CA operators.

The present paper seeks to illuminate the situation by addressing the following points:

Clarification of the actual philosophical positions of CA practitioners and intent of on-orbit CA activities, and the way this posture affects the use of dilution-region data in decision support;

Examination of some of the proposed alternatives to the use of the Pc for dilution-region situations and their operational viability; and

Treatment of how more, and more frequent, tracking data might ameliorate the situation, and what parts of the problem are likely to abide even with such improvements.

The paper will conclude with a set of recommendations for handling “dilution region” situations operationally.